The following U.S. patents are fully incorporated herein by reference: International Patent Application No. PCT/US99/23313 (Drzaic et al., xe2x80x9cEncapsulated Electrophoretic Displays Having a Monolayer of Capsulesxe2x80x9d); U.S. Pat. No. 4,143,103 (Sheridon, xe2x80x9cMethod of Making a Twisting Ball Panel Displayxe2x80x9d); U.S. Pat. No. 5,754,332 (Crowley, xe2x80x9cMonolayer Gyricon Displayxe2x80x9d); U.S. Pat. No. 5,815,306 (Sheridon et al., xe2x80x9cEggcrate Substrate for a Twisting Ball Displayxe2x80x9d); and U.S. Pat. No. 6,055,091 (Sheridon et al., xe2x80x9cTwisting-Cylinder Displayxe2x80x9d).
This invention relates generally to visual displays and more particularly to an apparatus and method of making ordered arrays for reusable, addressable, paper-like visual displays, such as gyricon displays and the like.
Typically, a display device, in sheet form, comprises a thin sheet, which has many attributes of a paper document. It looks like paper, has ambient light valve behavior like paper (i.e. the brighter the ambient light, the more easily it may be seen), is flexible like paper, can be carried around like paper, can be written on like paper, can be copied like paper, and has nearly the archival memory of paper.
There have been different approaches to making a display sheet such as U.S. Pat. No. 4,143,103 titled xe2x80x9cMethod of Making a Twisting Ball Panel Displayxe2x80x9d, in which a plurality of particles, which have an electrical anisotropy due to hemispherical surface coatings of different Zeta potential, are mixed with a light transparent liquid which is subsequently cured to form an elastomeric slab. Following curing of the liquid, the slab is immersed in a dielectric liquid, which is absorbed by the slab and which causes the slab to expand slightly. Expansion of the slab around the particles provides a plasticizer-filled cavity around each particle, allowing the particles to rotate to provide a display.
Alternatively, International Application No. PCT/US99/23313 titled xe2x80x9cEncapsulated Electrophoretic Displays Having a Monolayer of Capsulesxe2x80x9d teaches an encapsulated electrophoretic display constructed with a monolayer of capsules on a substrate. The capsules, which may be non-spherical, contain electrophoretically mobile particles and a suspending fluid. The electrophoretic particles are constrained to move within the capsule under the influence of an external electric field.
A closely packed gyricon display is described in U.S. Pat. No. 5,754,332 titled xe2x80x9cMonolayer Gyricon Displayxe2x80x9d, which discloses a layer of close-packed spheres suspended in an elastomer. The close-packed layer according to this disclosure is accomplished by using an elastomer cured with a 15-percent curing agent (hardener) at 90 degrees Celsius. Upon application of the dielectric fluid, the elastomer expands only 20 percent as compared to 50 percent or more through the conventional curing process. By varying the composition of the dielectric fluids, expansion of the elastomer may be reduced to approximately 10 percent. Interstices between the spheres may be filled with smaller spheres.
An alternate approach was disclosed in U.S. Pat. No. 5,815,306 titled xe2x80x9cEggcrate Substrate for a Twisting Ball Displayxe2x80x9d, in which the display includes a substrate having a cavity-containing matrix whose cavities are hollow cylindrical cells aligned with a lens array. Each cavity is filled with a transparent dielectric fluid and contains at most one optically anistropic particle, which is not attached to the substrate. The diameter and depth of the cavities are slightly larger than that of the particles. Each particle can have an anisotropy for providing an electrical dipole moment, with the electrical dipole moment rendering the particle electrically responsive. When the particle is rotatably disposed in an electric field while the electrical dipole moment of the particle is provided, the particle rotates to an orientation in which the electrical dipole moment aligns with the field.
Alternatively, U.S. Pat. No. 6,055,091 titled xe2x80x9cTwisting-Cylinder Displayxe2x80x9d, discloses a twisting-particle display based on nonspheroidal optically anisotropic particles disposed in a substrate. The particles can be bichromal cylinders, preferably aligned parallel to one another and packed close together in a monolayer. The substrate containing the cylinders can be fabricated with the swelled-elastomer techniques known from spherical-particle gyricon displays, with an agitation process step being used to align the cylinders within the sheet material.
A closely-packed monolayer display offers numerous advantages over a display containing randomly distributed spheres. Close-packed monolayer displays exhibit superior reflectance and brightness characteristics as compared with conventional gyricon displays, and the more of the monolayer plane that is covered by the gyricon elements, the better the reflectance and the brighter the display. However, the fabrication methods described in the art result in arrays having inter-sphere gaps, which negatively impact the reflectance and brightness characteristics of the display. A fabrication method is needed that would provide closely-packed ordered arrays with negligible inter-sphere gaps.
Briefly stated, and in accordance with one aspect of the present invention, there is provided a micro-structure template for fabricating ordered arrays of micro-particles. The template includes a top surface and a bottom surface, with a plurality of depressions disposed in the top surface. Particles are disposed in the depressions to form at least one layer of particles.